Abstract : The object of the invention is a device for deflecting a light beam based on the electro-optical effect is different in that, to increase the speed of response, it is made in the form of an elongated rectilinear parallelepiped composed of two or more trigonal prisms that are made from electro-optical crystals; the light strikes the face of the parallelepiped whose lateral sides are covered with electrodes. The device described in paragraph 1 is different in that, to use it as the light valve in a laser, it is placed between the external mirrors of the laser, which are set at an angle to each other. (Author)